Decoupler with tuned damping and methods associated therewith

ABSTRACT

In an aspect, the invention relates to a decoupler that is positionable between a shaft (eg. for an alternator) and an endless power transmitting element (eg. a belt) on an engine. The decoupler includes a hub that mounts to the shaft, and a pulley that engages the endless power transmitting element, an isolation spring between the hub and the shaft. The decoupler provides at least a selected damping torque between the hub and the pulley.

This application is a Continuation of U.S. patent application Ser. No.13/878,879 which is a national phase entry application ofPCT/CA2011/001263, filed Nov. 14, 2011, which claims the benefit of:U.S. Provisional Application No. 61/413,475, filed Nov. 14, 2010 andU.S. Provisional Application No. 61/414,682, filed Nov. 17, 2010, thecontents of all of which are incorporated herein by reference in theirentireties.

FIELD OF THE INVENTION

The present invention relates to decoupling mechanisms for allowing beltdriven accessories to operate temporarily at a speed other than thespeed of the belt, and more particularly to decoupling mechanisms foralternators.

BACKGROUND OF THE INVENTION

It is known to provide a decoupling mechanism on an accessory, such asan alternator, that is driven by a belt from the crankshaft of an enginein a vehicle. Such a decoupling mechanism, which may be referred to as adecoupler assembly or a decoupler, permits the associated accessory tooperate temporarily at a speed that is different than the speed of thebelt. As is known, the crankshaft undergoes cycles of accelerations anddecelerations associated with the firing of the cylinders in the engine.The decoupler permits the alternator shaft to rotate at a relativelyconstant speed even though the crankshaft from the engine, and hence,the pulley of the decoupler, will be subjected to these same cycles ofdecelerations and accelerations, commonly referred to as rotarytorsional vibrations, or torsionals.

Such a decoupler is a valuable addition to the powertrain of thevehicle. However, some engines are harsher on the decoupler than otherengines and decouplers on such engines do not last as long as wouldotherwise be desired. It would be advantageous to provide a decouplerthat worked on such engines.

SUMMARY OF THE INVENTION

In an aspect, the invention relates to a decoupler that is positionablebetween a shaft (eg. for an alternator) and an endless powertransmitting element (eg. a belt) on an engine. The decoupler includes ahub that mounts to the shaft, and a pulley that engages the endlesspower transmitting element, an isolation spring between the hub and theshaft. The decoupler provides at least a selected damping torque betweenthe hub and the pulley.

The damping torque may be selected to provide less than a selectedmaximum amount of torsional vibration to the hub of the decouplerparticularly in a selected frequency range. In particular providing lessthan the selected maximum amount of torsional vibration to the hub ofthe decoupler in the selected frequency range is useful when thedecoupler is connected to a shaft of an alternator. It has been foundthat this inhibits the voltage regulator of the alternator fromcontrolling the alternator at a switching frequency that is in the rangeof 15 Hz, which may be near the natural frequency of the decoupler.Inhibiting the alternator from having such a switching frequency reducesany torsional vibration induced in the hub from the alternator, in thatfrequency range. This reduces the overall torsional vibration incurredby the hub, which improves the fatigue life of the isolation spring.

Through significant testing it has been found that the voltage regulatorof the alternator may be upset by current fluctuations that result fromfirst order vibrations that are incurred by the alternator rotor. Whenthis occurs, the voltage regulator itself may switch to a switchingfrequency in the range of about 15 Hz. When it does this, it generates avibration in the alternator rotor that it transmitted back into the hubof the decoupler. Because this frequency is near the natural frequencyof the decoupler the hub may respond with a significantly increasedamplitude of vibration (i.e. the hub will reciprocate through a higherangular range). This increased angular range of reciprocation cansignificantly increase the stressed on the isolation spring in thedecoupler and thereby reduce its fatigue life. By damping the vibrationsfrom the engine, and in particular the first order vibrations so thatthey are attenuated by a selected amount before reaching the hub (andtherefore before they reach the alternator rotor) the voltage regulatoris less likely to respond to the current fluctuations generated therebywith a switching frequency in the 15 Hz range. Thus the voltageregulator will have a reduced tendency of feeding more vibration backinto the alternator rotor and the hub of the decoupler at frequenciesnear the natural frequency of the hub.

In a particular embodiment, the decoupler includes, a hub, a pulley, anisolation spring, a first friction surface, a second friction surfaceand a retainer. The hub is adapted to be coupled to the shaft such thatthe shaft co-rotates with the hub about a rotational axis. The pulley isrotatably coupled to the hub and has an outer periphery that is adaptedto engage the endless power transmitting element. The isolation springis positioned to transfer rotational force from the pulley to the huband to accommodate torsional vibration between the pulley and the hub.The first friction surface is operatively connected with the pulley. Thesecond friction surface is operatively connected with the hub. Thefriction surface biasing member is positioned for exerting a biasingforce to biasing the first and second friction surfaces against eachother. The retainer is engaged with the friction surface biasing memberand positioned to cause the friction surface biasing member to apply atleast a selected biasing force on the first and second friction surfacesthereby generating at least a selected damping torque during relativerotational movement between the pulley and the hub.

The damping structure biasing member may be a Belleville washer, whichmay have any suitable number of waves to suit the application.Alternatively, the damping structure biasing member may be a helicalcompression spring. As a further alternative, the damping structurebiasing member may be one of a plurality of helical compression springs.In such an alternative embodiment, the damping structure may furtherinclude a support member that has the friction member on one side and aplurality of blind apertures or other spring supports on the other sidefor receiving and supporting the compression springs, such that theplurality of damping structure biasing members each are positionedindependently of one another to urge the friction member in parallelwith one another. In another alternative embodiment, a plurality ofdamping structure biasing members could be arranged in series with oneanother (e.g. end-to-end).

In an aspect, the invention relates to a test decoupler for use inhelping to produce a production decoupler. The test decoupler ispositionable between a shaft (eg. for an alternator) and an endlesspower transmitting element (eg. a belt) on an engine or on a test setupintended to simulate an engine. The test decoupler includes a hub thatmounts to the shaft, and a pulley that engages the endless powertransmitting element, an isolation spring between the hub and the shaft.The test decoupler is capable of adjusting the amount of damping torqueit produces between the hub and the pulley. In this way it can be usedto help determine a suitable damping torque to provide in the productiondecoupler.

In an embodiment, the test decoupler includes, a hub, a pulley, anisolation spring, a first friction surface, a second friction surfaceand a retainer. The hub is adapted to be coupled to the shaft such thatthe shaft co-rotates with the hub about a rotational axis. The pulley isrotatably coupled to the hub and has an outer periphery that is adaptedto engage the endless power transmitting element. The isolation springis positioned to transfer rotational force from the pulley to the huband to accommodate torsional vibration between the pulley and the hub.The first friction surface is operatively connected with the pulley. Thesecond friction surface is operatively connected with the hub. Thefriction surface biasing member is positioned for exerting a biasingforce to biasing the first and second friction surfaces against eachother. The retainer is engaged with the friction surface biasing member.The position of the retainer controls the biasing force of the frictionsurface biasing member. The retainer is adjustable in position.

In another aspect, the invention is directed to a method of producing aproduction decoupler for an engine, comprising:

-   a) providing resonance data associated with the engine;-   b) determining using software an approximate damping torque to    provide a selected amount of damping between a hub and a pulley of    the production decoupler based on the resonance data provided in    step a);-   c) providing a test decoupler that is capable of providing an    adjustable damping torque including the approximate damping torque    determined in step b);-   d) selecting a final damping torque to be provided by the production    decoupler by applying torsional vibrations on the test decoupler,    based on the resonance data of step a); and-   e) producing the production decoupler that includes a production hub    that is adapted to be coupled to a shaft such that the shaft    co-rotates with the hub about a rotational axis, a pulley rotatably    coupled to the hub and having an outer periphery that is adapted to    engage an endless power transmitting element driven by the engine,    and an isolation spring positioned to transfer rotational force from    the pulley to the hub and to accommodate torsional vibration between    the pulley and the hub, wherein the production decoupler applies at    least the final damping torque between the production hub and the    production pulley.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the attached drawings, in which:

FIG. 1 is an elevation view of an engine with a plurality of belt drivenaccessories, one of which has a decoupler in accordance with anembodiment of the present invention;

FIG. 2 is an exploded perspective view of the decoupler shown in FIG. 1;

FIG. 3 is a magnified sectional view of the decoupler shown in FIG. 2;

FIG. 4 is a magnified sectional view of a variant of the decoupler shownin FIG. 2;

FIG. 5 is a magnified sectional view of another variant of the decouplershown in FIG. 2,

FIG. 6 is a magnified sectional view of another variant of the decouplershown in FIG. 2;

FIG. 7a is a graph showing the vibration response of the pulley and hubfrom the decoupler of FIG. 1 over a range of frequencies;

FIG. 7b is a graph showing the torque response of the decoupler of FIG.1 in relation to relative displacement between the pulley and hub;

FIG. 8 is a magnified sectional view of a test decoupler that is capableof adjustable damping torque for use in designing the decoupler shown inFIG. 1, in accordance with another embodiment of the invention;

FIG. 9 is a flow diagram of a method of producing a decoupler, inaccordance with another embodiment of the invention;

FIG. 10 is a magnified sectional view of a decoupler that is capable ofadjustable damping torque and including an actuator for adjustment ofthe damping torque, in accordance with another embodiment of theinvention;

FIG. 11 is a magnified sectional view of a portion of the decouplershown in FIG. 10; and

FIG. 12 is a magnified sectional view of another decoupler that iscapable of adjustable damping torque and including an actuator foradjustment of the damping torque, in accordance with another embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1, which shows an engine 10 for a vehicle. Theengine 10 includes a crankshaft 12 which drives an endless driveelement, which may be, for example, a belt 14. Via the belt 14, theengine 10 drives a plurality of accessories 16 (shown in dashedoutlines), such as an alternator 18. Each accessory 16 includes an inputdrive shaft 15 with a pulley 13 thereon, which is driven by the belt 14.A decoupler 20 is provided instead of a pulley, between the belt 14 andthe input shaft 15 of any one or more of the belt driven accessories 16,an in particular the alternator 18.

Reference is made to FIG. 2, which shows a sectional view of thedecoupler 20. The decoupler 20 includes a hub 22, a pulley 24, a firstbearing member 26, a second bearing member 27, an isolation spring 28, acarrier 30, and a one-way clutch 31, which in this exemplary embodimentis a one-way wrap spring clutch comprising a wrap spring 32.

The hub 22 may be adapted to mount to the accessory shaft 15 (FIG. 1) inany suitable way. For example, the hub 22 may have a shaft-mountingaperture 36 therethrough that is used for the mounting of the hub 22 tothe end of the shaft 15, for co-rotation of the hub 22 and the shaft 15about an axis A.

The pulley 24 is rotatably coupled to the hub 22. The pulley 24 has anouter surface 40 which is configured to engage the belt 14. The outersurface 40 is shown as having grooves 42. The belt 14 may thus be amultiple-V belt. It will be understood however, that the outer surface40 of the pulley 24 may have any other suitable configuration and thebelt 14 need not be a multiple-V belt. For example, the pulley 24 couldhave a single groove and the belt 14 could be a single V belt, or thepulley 24 may have a generally flat portion for engaging a flat belt 14.The pulley 24 further includes an inner surface 43, which the wrapspring 32 may engage in order to couple the pulley and hub 22 together.The pulley 24 may be made from any suitable material, such as a steel,or aluminum, or in some cases a polymeric material, such as certaintypes of nylon, phenolic or other materials.

The first bearing member 26 rotatably supports the pulley 24 on the hub22 at a first (proximal) axial end 44 of the pulley 24. The firstbearing member 26 may be any suitable type of bearing member, such as abushing made from nylon-4-6 or for some applications it could be PX9Awhich is made by DSM in Birmingham, Mich., USA, or some other suitablepolymeric material, and may be molded directly on the pulley 24 in a twostep molding process in embodiments wherein a molded pulley is provided.It may be possible to use a bearing (e.g. a ball bearing) as the firstbearing member 26 instead of a bushing. In such a case, the bearingcould be inserted into a mold cavity and the pulley 24 could be moldedover the bearing 26. Instead of a bearing, a metallic (e.g. bronze)bushing may be provided, which can be inserted into a mold cavity forthe pulley molding process in similar fashion to the aforementionedbearing.

The second bearing member 27 is positioned at a second (distal) axialend 46 of the pulley 24 so as to rotatably support the pulley 24 on apulley support surface 48 of the hub 22. The second bearing member 27may mount to the pulley 24 and to the hub 22 in any suitable ways. Inthe embodiment shown, the second bearing member 27 may be molded aroundthe pulley support surface 48 by an injection molding process whereinthe hub 22 forms part of the mold. The hub 22 may have a coating thereonprior to insertion into the mold cavity, to prevent strong adherence ofthe bearing member 27 to the pulley support surface 48 during themolding process, so that after removal of the hub 22 and bearing member27 from the molding machine (not shown), the bearing member 27 canrotate about the hub 22. The bearing member 27 may be press-fit into aseat 49 on the pulley 24, and may be welded (e.g. laser welded) with thepulley 24 in embodiments wherein the pulley 24 is made from a suitablepolymeric material. In such instances, the material of the pulley 24 andthe material of the first bearing member 26 are selected so as to becompatible for joining by whatever suitable joining process is selected,such as laser welding. It will be noted that other ways of joining thesecond bearing member 27 and the pulley 24 may be employed, such asadhesive bonding, and/or using mechanical joining elements (e.g.resilient locking tabs) that would lock the bearing member 27 to thepulley.

The isolation spring 28 is provided to accommodate oscillations in thespeed of the belt 14 relative to the shaft 15. The isolation spring 28may be a helical torsion spring that has a first helical end 50 that isheld in an annular slot and that abuts a radially extending driver wall52 (FIG. 3) on the carrier 30. The isolation spring 28 has a secondhelical end 53 (FIG. 2) that engages a similar driver wall (not shown)on the hub 22. In the embodiment shown, the isolation spring 28 has aplurality of coils 58 between the first and second ends 50 and 53. Thecoils 58 are preferably spaced apart by a selected amount and theisolation spring 28 is preferably under a selected amount of axialcompression to ensure that the first and second helical ends 50 and 53of the spring 28 are abutted with the respective walls on the carrier 30and hub 22. An example of a suitable engagement between the isolationspring 28, the hub 22 and the carrier 30 is shown and described in U.S.Pat. No. 7,712,592, the contents of which are incorporated herein byreference. A thrust plate 73 may be provided to receive the axial thrustforce of the carrier 30 resulting from the axial compression of thespring 28.

The isolation spring 28 may be made from any suitable material, such asa suitable spring steel. The isolation spring 28 may have any suitablecross-sectional shape. In the figures, the isolation spring 28 is shownas having a generally rectangular cross-sectional shape, which providesit with a relatively high torsional resistance (i.e. spring rate) for agiven occupied volume. However, a suitable spring rate may be obtainedwith other cross-sectional shapes, such as a circular cross-sectionalshape or a square cross-sectional shape.

Alternatively, the isolation spring 28 may be compression spring. As afurther alternative, the isolation spring 28 may be one of two or moreisolation springs, each of which is a compression spring. Such aconfiguration is shown in U.S. Pat. No. 7,708,661 and US Patentapplication publication no. 2008/0312014, PCT publication no.2007/074016, PCT publication no. 2008/022897, PCT publication no.2008/067915, and PCT publication no. 2008/071306, all of which arehereby incorporated by reference in their entirety.

In the embodiment shown in FIG. 2, a sleeve 57 is provided between theisolation spring 28 and the clutch spring 32. The sleeve 57 is, in theembodiment shown, a helical member itself, although it could have anyother suitable configuration such as a hollow cylindrical shape. Thesleeve 57 acts as a torque limiter by limiting the amount of roomavailable for radial expansion of the isolation spring 28 (inembodiments wherein the isolation spring 28 is a torsion spring). Thuswhen a torque is provided by the pulley 24 that exceeds a selectedlimit, the isolation spring 28 expands until it is constrained by thesleeve 57. An example of a suitable sleeve 57 is shown and described inU.S. Pat. No. 7,766,774, the contents of which are hereby incorporatedby reference.

The helical clutch spring 32 has a first end 51 that is engageable witha radial wall 55 of the carrier 30 and that may be fixedly connected tothe carrier 30. The helical clutch spring 32 has a second end 59 thatmay be free floating.

The carrier 30 may be made from any suitable material such as, forexample, a suitable nylon or the like.

When a torque is applied from the belt 14 to the pulley 24 to drive thepulley 24 at a speed that is faster than that of the shaft 15, frictionbetween the inner surface 43 of the pulley 24 and the coils of theclutch spring 32 drives at least one of the coils of the clutch spring32 at least some angle in a first rotational direction about the axis A,relative to the first end 51 of the clutch spring 32. The relativemovement between the one or more coils driven by the pulley 24 relativeto the first end 51 causes the clutch spring to expand radially, whichfurther strengthens the grip between the coils of the clutch spring 32and the inner surface 43 of the pulley 24. As a result, the first end 59of the clutch spring 32 transmits the torque from the pulley to thecarrier 30. The carrier 30 transmits the torque to the hub 22 throughthe isolation spring 28. As a result, the hub 22 is brought up to thespeed of the pulley 24. Thus, when the pulley 24 rotates faster than thehub 22, the clutch spring 32 operatively connects the pulley 24 to thecarrier 30 and therefore to the hub 22.

At the distal end of the hub 22 is a first friction surface 60 thatengages a second friction surface 62 on a friction member 64. Thefriction member 60 is operatively connected to the hub 22 (in thisparticular instance it is directly on the hub 22). The friction surface62 is operatively connected to the pulley 24. In this exemplaryembodiment it is on the friction member 64, which is adjacent to andaxially and rotationally coupled to a thrust washer 66. A frictionsurface biasing member 68 is engaged axially and rotationally with thethrust washer 66 and is retained in place by a retainer member 69, and aseal cap 71 is provided to cover the distal end to prevent intrusion ofdirt and debris into the interior space of the decoupler 20. The biasingmember 68 urges the friction surfaces 60 and 62 into engagement witheach other with a selected force. This selected force directly affectsthe frictional force that the friction surfaces 60 and 62 exert on eachother. The biasing member 68 in FIGS. 2 and 3 is a Belleville washer 70.However, it will be understood that other types of biasing member couldbe used, such as for example, a helical compression spring 72 as shownin FIG. 4, a plurality of compression springs 74 as shown in FIG. 5, ora monolithic elastomeric biasing member 76 as shown in FIG. 6. Each ofthe friction member 64, the thrust member 66, the biasing member 68 andthe retainer 69 may be fixed rotationally with the pulley 24 by anysuitable means. For example, they may each have a radial protrusion thatextends into an axially extending slot in the pulley 24. It will also benoted that in the embodiments shown in FIGS. 4, 5 and 6 there is anadditional thrust plate (not numbered) between the retainer 69 and thebiasing member 68 to assist with the distribution of force between them.

In each of these embodiments, the biasing member 68 is positioned sothat a selected normal force is applied on the friction surfaces 60 and62. Additionally, the materials that make up the first and secondfriction surfaces 60 and 62 and the surface finishes provided on thesesurfaces 60 and 62 are selected so that these surfaces have a selectedcoefficient of friction. By providing a selected coefficient of frictionbetween the surfaces 60 and 62 and by providing a selected normal force,a selected frictional force is exerted on the hub 22.

In the particular embodiment shown, the friction member 64 is engagedwith the hub 22 directly. It is possible for the friction member 64 toengage the hub 22 indirectly (e.g. through engagement with a frictionsurface on another member that is itself connected directly to the hub22).

The selected frictional force may be referred to as a selected dampingforce, which exerts a selected damping torque on the hub 22. The purposeof this selected damping torque is described below.

When an engine, such as engine 10, operates it is well known that thecrankshaft speed oscillates between high and low values about a meanspeed. The mean speed of the crankshaft 12 depends, of course, on theRPM of the engine. The speed variations of the crankshaft are aninherent property of internal combustion engines due to the firing ofthe cylinders, which generates linear motion in the pistons, which istransferred to the crankshaft 12 via connecting rods. These speedvariations of the crankshaft 12 are transferred to the crankshaftpulley, from the crankshaft pulley into the belt 14, and from the belt14 to the decoupler pulley 24.

For a 4-cylinder engine the crankshaft 12 (and therefore the decouplerpulley 24) undergo second-order vibrations. That is to say, thefrequency of the vibration of the pulley 24 is the speed of the engine xthe number of cylinders/2. Thus, for a 4-cylinder engine at idle (e.g.about 750 RPM), the decoupler pulley 24 undergoes vibration at 750rotations/minute×1 minute/60 seconds×4/2=25 Hz.

Reference is made to FIGS. 7a and 7b , which show test results from atest performed on a test bench configured to simulate the driving of thealternator 18 through a front engine accessory drive of the type that iscommonly employed in vehicles, that is driven by a 4-cylinder engine atidle. Referring to FIG. 7a , the curve shown at 80 represents the amountof angular oscillation that the pulley 24 undergoes in relation tofrequency. As can be seen, and as expected, at a frequency of about 25Hz, there is a peak 82 in the curve 80 indicative of a vibration ofabout 8 degrees peak-to-peak. One can observe, however, that there is a(much smaller) peak shown at 84 at about 12.5 Hz indicative of a pulleyvibration of less than a degree peak-to-peak. This is an unexpectedfirst order vibration, which may be due to several factors, such as animbalance in the crankshaft or some other component in the FEAD system.An additional cause of such first order vibrations however, occursparticularly in diesel engines. To optimize catalytic converterfunction, such engines may alternate between rich and lean firings. Thisgenerates a torque pulse twice per cycle on a 4-cylinder, which meansonce per rotation of the crankshaft. This is therefore a first ordervibration.

The curve shown at 86 in FIG. 7a represents the amount of angularoscillation that the hub 22 undergoes in relation to frequency. Asexpected, there is a peak 88 at about 25 Hz that is the result of thepulley oscillation at 25 Hz. The amplitude of the oscillations at 25 Hzis about 4 degrees peak-to-peak. This is expected given the approximatediameter ratio of the pulley 24 to the hub 22. However, it can be seenthat there is also a peak 90 at the first order frequency (i.e. 12.5 Hzin this case). This peak 90 shows that very small vibrations at thepulley 24 (i.e. less than 1 degree) result in unexpectedly largevibrations at the hub 22 (about 5.5 degrees peak-to-peak).

Further analysis revealed that what appears to be occurring is that thealternator's voltage regulator, changes its switching frequency incertain situations to a frequency that is in the range of about 15 Hz.The voltage regulator controls the voltage output of the alternator 18,keeping the voltage constant regardless of changes in engine speed (andtherefore alternator rotor speed) and electrical load. To carry thisout, the voltage regulator cyclically activates and deactivates thevoltage at the excitation windings thereby controlling the ratio of ontime to off time so as to adjust the output voltage based on the voltagegenerated in the alternator. The voltage regulator is controlled basedon a number of inputs, and as such a number of situations can affect theactions of the voltage regulator. For example, rotor speed fluctuationcan cause fluctuations in the current generated by the alternator. Thiscan cause the voltage regulator to change (drop) the switching frequencyto compensate for the fluctuating current.

This effect on the voltage regulator is particularly strong when thereare first order vibrations transferred into the decoupler 20 from theengine 10. When exposed to these first order vibrations in particularthe voltage regulator may react by changing the switching frequency to afrequency in the range of about 15 Hz.

The switching of the voltage regulator causes a certain amount oftorsional vibration in the alternator rotor and shaft, which istransferred into the hub 22 of the decoupler 20. Thus, the oscillationsthat result in the hub 22 are partly caused by the oscillations in thepulley 24 and partly caused by the oscillations in the alternator shaft(shown at 94 in FIG. 1). It will be noted that the decoupler 20 may havea natural resonance frequency that is somewhere in the range of about 5Hz to about 20 Hz, or more precisely from about 12 Hz to about 15 Hz.Vibrational inputs to the hub 22 that are near the natural resonancefrequency of the decoupler 20 can become magnified. As noted above, theswitching frequency of the voltage regulator may be in the range of 15Hz in some situations when the voltage regulator is affected by thefluctuations in the rotor speed. Thus the hub 22 can be subjected totorsional vibrations from the alternator shaft at a frequency that isnear the natural frequency of the decoupler 20. Also as noted above,there can be first order vibrations (which are near the naturalfrequency of the decoupler 20 when the engine is at idle) which aretransmitted to the pulley 24 and through to the hub 22, which are theresult of imbalances in the crankshaft 12 and the like.

The amount of damping torque provided in the exemplary decoupler 20whose performance is shown in FIG. 7a is here is 0.29 in overrunningmode (i.e. when the hub 22 overruns the pulley 24). In non-overunningmode the damping torque is half of the difference in the upper and lowerportions of the torque curve shown at 89 in FIG. 7 b.

The torsional vibrations at the hub 22 that are near the naturalfrequency of the decoupler 20 and which therefore may get magnified canimpact the operating life of the decoupler 20, and in particular theoperating life of the isolation spring 28. The particular amount oftorsional vibration that would be considered acceptable will vary fromapplication to application. It is possible that the operating life ofthe decoupler 20 may be considered to be acceptable even though there isa 5.5 degrees peak-to-peak oscillation when the engine is at idle. Itdepends of course on many factors, such as the material of constructionof the components that make up the decoupler 20, and the number ofoperational cycles that would constitute an acceptable operating life.The operating life may, however, be considered too short. It has beendetermined that a way of extending the operating life of the decoupler20 is to reduce the amplitude of vibration of the hub 22.

Thus, it is possible when designing the decoupler to start by selectinga suitable operating life for it, then to decide what maximum amplitudeof vibration in the hub 22 is acceptable. The amplitude of vibration canbe controlled via damping. The amount of damping that is required may beestablished empirically, by running mathematical models, or by any othersuitable method. In an embodiment, the mathematical models would be runfirst. The results from those models could be used to produce a testdecoupler that is capable of adjustable damping. This test decoupler isshown at 100 in FIG. 8. This test decoupler 100 may have many componentssimilar to those on the decoupler 10 shown in FIG. 2, such as a hub 122,a pulley 124, an isolation spring 128, a wrap spring 132, a sleeve 157,bearing members 126 and 127, a thrust member 166, a friction member 164with a friction surface 162 thereon for engagement with friction surface160 on the hub 122, and may further include some additional structure.For example, the decoupler 100 includes a biasing member 102 that ismade up of a plurality of Belleville washers 70. Furthermore, theretainer, shown at 104 is axially adjustable in position by means of athreaded exterior surface 106 on the retainer 104, that mates with athreaded surface 107 on the pulley shown at 124. The threaded surfaces106 and 107 also provide structure with which the retainer 104 is heldin whatever position it is adjusted to. By providing the test decoupler100, the damping torque applied in the decoupler 100 can be easily setto the value determined by the mathematical models, and can then beadjusted up or down quickly in situ if it is determined that theoscillations are too large. The oscillations can be measured duringtesting using a number of different types of sensor that can provideprecise information relating to the angular position of the pulley 124and the hub, shown at 22. For example, the 2SA-10 Sentron sensormanufactured by Sentron AG, Baarerstrasse 73, 630O Zug, Switzerland is asuitable sensor that can be used to measure the torsional vibrations.Use of such a sensor to measure torsional vibrations is described in PCTpublication WO2006/045181 the contents of which are incorporated hereinby reference. The sensor for the pulley 124 is shown at 108 and thesensor for the hub 122 is shown at 110. Sensor 110 is shown at theopposite end of alternator shaft 15 (i.e. at the opposite end to the endthat the decoupler 100 is mounted to).

A controller 111 may be provided to receive signals from the sensors 108and 110 and can indicate to an operator what the torsional vibrationsare. The operator can then adjust the position of the retainer 104 onthe decoupler 100 to increase or decrease the damping force until thetorsional vibrations at the hub 122 are below the determined limit (i.e.are below the maximum amplitude of vibration calculated for the desiredoperating life). Alternatively the system could be automated so that thecontroller 111 controls the retainer 104 and positions it as necessaryto achieve less than a selected torsional vibration at the hub 122.

This test decoupler 100 may be used to assist in carrying out a methodof producing the production decoupler 20. The method includes:

a) providing resonance data associated with the engine;

b) determining using software an approximate damping torque to provide aselected amount of damping between a hub and a pulley of the productiondecoupler 20 based on the resonance data provided in step a);

c) providing a test decoupler (i.e. the test decoupler 100) that iscapable of adjustable damping torque;

d) determining a suitable damping torque for use with the productiondecoupler 20 using the test decoupler 100, based on the approximatedamping torque determined in step b); and

e) producing the production decoupler 20 with a production hub 22, aproduction pulley 24, a production friction member 64 and a productionbiasing member 68 that is positioned and held to generate a biasingforce on the friction member 64 so that the friction member 64 providesat least the suitable damping torque between the hub 22 and the pulley24. These steps are shown at 201, 202, 204, 206 and 208 respectively inthe flow diagram shown in FIG. 9, relating to a method 200. It will benoted that it is at least conceivable that step b) could be omitted, andthat step d) could be carried out simply by progressively increasing thedamping torque until a selected result is observed. For example, thedamping torque can be increased until any torsional vibration observedin the hub 122 is less than a selected level.

In step a), providing the resonance data may be achieved by receivingthe resonance data from a manufacturer of the engine, or alternativelyby receiving an example engine from the manufacturer and testing it andmeasuring the resonance. Providing the resonance data may also becarried out as follows. A customer (eg. an engine manufacturer)initially gives the entity that is manufacturing the decoupler 20 (whichmay simply be referred to as ‘the entity’), some preliminary engineeringdata related to the inertia of various components on the engine relatingto the drive of the endless power transmitting element. Also thecustomer may give the entity projected loads and load profiles (steadyfrictional load, or periodic pulsating load) of each component andinformation regarding the endless power transmitting element, such asbelt stiffness if it is a belt. The entity takes the data and conducts apreliminary analysis using software such as a simulation program. Thepreliminary analysis results in an initial design for the productiondecoupler 20 including an approximate spring rate for the productionisolation spring 28 for reducing the severity of the resonancesdescribed by the resonance data, a maximum permissible angular vibrationin order to maintain a minimum fatigue life for the isolation spring 28,and a prediction of an approximate damping torque that needs to beprovided by the production decoupler 20 to achieve the desired fatiguelife. Several design iterations may be traded back and forth between thecustomer and the entity during the process of designing and building aprototype engine.

The entity then refines the prediction of the minimum damping torque byconducting tests using the test decoupler 100 in FIG. 8. Preferably thetests are conducted on the actual vehicle containing the actual engineon which the production decoupler 20 will be provided. This permitstesting over the most complete range of scenarios (idling while certainbelt driven accessories are on, such as the A/C compressor, and whilecertain electrical accessories are on such as the lights), and caninclude the actual ECU with its final programming (or as close to it asis available). This is useful because the ECU can provide useful data tothe person adjusting the test decoupler 100, such as, for example,alternator current, power steering pressure, A/C pressure, and the like.Additionally, the voltage regulator is in many modern vehicles no longera separate component. Its function is instead carried out by the ECU. Ifa complete vehicle is not available for testing, an option is to use atest engine.

Sensors, such as, for example a Rotec sensor by SCHENCK RoTec GmbH ofDarmstadt, Germany, may be provided for detecting the angular positionsof the pulley 124 and the hub 122 during the above described testingwith the test decoupler 100. Using such sensors, the test decoupler 100can be adjusted in its damping torque (e.g. by adjustment of theretainer to progressively increase the biasing force on the frictionmember 164) until the angular vibration of the hub 122 falls below themaximum permissible angular vibration to achieve the minimum desiredfatigue life for the spring 28. For example, the damping torque may beincreased until the angular vibration observed at the hub 122 fallsbelow 1 degree peak-to-peak. It has been observed that providing asuitable amount of damping has a particularly beneficial effect inrelation to first order vibrations. More particularly, by damping outfirst order vibrations transmitted from the engine before they reach thehub 22 (i.e. between the pulley 24 and the hub 22), the aforementionedcurrent fluctuations that occur in the alternator appear to be lower andthe voltage regulator appears to have a reduced tendency to react with aswitching frequency in the 15 Hz range. As a result, the voltageregulator would contribute less to the vibrations of the hub 22 in thatfrequency range.

If an engine is not available then an option would be to acquire thecomponents only, such as the alternator, the power steering pump, theA/C compressor, and whatever other accessories are driven by the belt.These components would be mounted onto a thick metal backing plate inthe correct X, Y and Z positions (i.e. in the positions they will bemounted in when in the production vehicle), and would be connected andcontrolled to generate the correct loads (eg. power steering pressure,A/C pressure, etc.) when rotated. This mounting plate may be assembledto a large servo-hydraulic rotary torsional actuator drive system,manufactured by servo-hydraulic companies such as MTS SystemsCorporation of Eden Prairie, Minn., USA, Team Machine Tools Inc. ofConcord, Ontario, Canada, or Horiba Automotive Test Systems Inc, ofBurlington, Ontario, Canada. The driveshaft of the servo-hydraulicrotary torsional actuator drive system may spin the crankshaft from idle(eg. about 600 RPM) to redline (eg. about 7,000 RPM), while imputingsimulated torsional vibrations into the belt drive in order to simulatethe primary combustion cycle torsional vibration input (e.g. asecond-order vibration for a four cylinder engine), and the upper orderharmonic vibrations, in order to simulate the operation of a realengine.

During such a test, the torsional vibration within the system may bemeasured at each major component using any suitable means such as atorsional rotary vibration measurement system, or TRVMS, (which is ineffect a sophisticated FFT (fast Fourier transform) analyzer), which isdesigned specifically for the analysis of rotary torsional vibrations atmultiple shafts.

Other quantities may be measured, such as instantaneous belt spantension within each belt span between pulleys (eg. using hub-loadsensors), belt span flutter (eg. using lasers or microwave radarsensors), belt tensioner arm oscillation deflection (using suitablesensors), as well as the instantaneous load of each pulley (alternatorcurrent, power steering pressure, A/C pressure, etc.).

With these measurements the entity determines the overall ‘health’ ofthe belt drive (while ‘belt’ is used in some instances, it willunderstood that the endless power transmitting element may be somethingother than a belt) under several real life conditions which can beprogrammed and simulated into the MTS servo-hydraulic test machine tomimic the torsional vibrations of the crankshaft.

In such a test, the adjustable test decoupler 100 uses a very finethread 106 machined into the inner diameter of the lead-in collar (thelead-in collar is the uppermost portion of the pulley 124) so as topermit fine axial adjustment of the retainer 104.

A “drive nut” (i.e. the retainer 104) can be threaded into or out of thethreaded lead-in collar by rotating the drive nut in a clockwise orcounter-clockwise fashion, thereby adjusting its axial position. Thethreaded drive nut 104 can be stopped and temporarily locked in anyposition within the threaded collar, by the use of a secondary locknutin the threaded collar.

The damping ratio (and therefore the damping force and the dampingtorque) within the test decoupler 100 can be increased by turning thedrive nut 104 down onto the wave washer to increase the biasing forceexerted by biasing member 102. The damping ratio (and therefore thedamping force and the damping torque) can be decreased by backing thedrive nut 104 out, decreasing the biasing force exerted by the biasingmember 102 on the test friction member 164.

During this test, a variety of different wave washers (Bellevillewashers) with higher or lower spring rates could be employed.Additionally, a variety of different frictional damping components couldbe employed, using materials with greater or lesser frictioncoefficients and longevity characteristics.

Many other tests may be performed by the entity on the endless powertransmission element itself, in order to determine its exact mechanicalproperties (eg. lateral and linear spring rates, stiffness, frictionalvalues, belt stretch, etc).

Once the retainer 104 has been adjusted successfully to provide anangular vibration at the hub 122 that is sufficiently low, the testdecoupler 100 may be mounted in a system where the torque exerted by thedecoupler 100 and the biasing force exerted by the biasing member 102can be measured. A torque curve similar to the curve xx in FIG. 7b maybe generated. Once this data is known, a design for the productiondecoupler 20 can be made, wherein particular materials and surfacefinishes can be selected for use in the first and second frictionsurfaces 60 and 62, and the biasing member 68 and its biasing force canbe selected so as to achieve the particular damping torque that isdesired. An example of a material that may, for some applications, besuitable on the friction surface 62 of the friction member 64 is EkaGripby Ceradyne Inc. of Costa Mesa, Calif., USA. The prototype can then betested on a production engine and preferably in a production vehicle toverify that is provides less than the maximum the desired angularvibration on the hub 22.

It will be noted that the production decoupler 20 need not be adjustablein terms of its damping force and damping torque.

The adjustable damping arrangement shown and described on the testdecoupler 100 may be applied to other types of decouplers, such as thosedescribed in U.S. Pat. Nos. 5,156,573, 7,766,774, 7,153,227, 7,591,357,7,624,852, all of which are incorporated herein by reference in theirentirety.

In some embodiments it may be possible to employ two or more differenttypes of biasing member together, such as, for example, a Bellevillewasher in conjunction with (i.e. in series with or in parallel with)either a single helical compression spring or multiple helicalcompression springs.

Several other combinations and permutations would be possible also,depending upon the packaging space available for the pulley length anddiameter.

While automotive alternator decoupler pulleys are sometimes severelylimited in both length and diameter due to underhood packagingconstraints, the invention may be applicable to much larger engineapplications, such as engines for buses, trucks, military, commercial,construction and industrial engine applications, which may be moretolerant to larger envelope packages. Such engines may permit the largerconfigurations of the biasing members 68 depicted in FIGS. 4, 5 and 6.Another solution where space is limited may be to provide a hollow shaftfor the alternator, and to provide an inner shaft within an outer shaftfor the alternator. The outer shaft would be connected to the rotor ofthe alternator. The pulley 24 would be fixedly mounted to the innershaft. The rest of the decoupler 20 would be provided to connect theinner and outer shafts, at the opposite end of the alternator to endwith the pulley 24.

When manufacturing the decoupler 20, the position of the retainer 69impacts the biasing force exerted by the biasing member 68 on thefriction member 64, which, as noted above, impacts the damping torqueprovided by the friction surfaces 60 and 62. To ensure that the retainer69 is positioned in a suitable position so that the desired dampingtorque is provided, the manufacture of the decoupler 20 can entail:

a) providing an assembly comprising the hub 22, the friction member 64,the thrust member 66 and the biasing member 68;

b) measuring the biasing force exerted by the biasing member 68;

c) compressing (or more generally, flexing) the biasing member 68 toprogressively increase the biasing force against the friction member 64until the measured biasing force reaches a selected value; and

d) fixing the retainer 69 in position to maintain the amount of flexure(compression) reached in step c).

Instead of measuring the biasing force and fixing the retainer 69 when aselected force is reached, the process may involve:

a) measuring the amount of compression or flexure in the biasing member68;

b) compressing it until a selected amount of flexure/compression isreached; and

c) fixing the retainer 69 in position to maintain the amount of flexure(compression) reached in step b).

Fixing the retainer 69 may be achieved, for example, by staking theretainer 69 in place in the pulley 24, or by crimping a lip of thepulley 24 into engagement with the retainer 69 to hold the retainer 69in place. Some types of biasing member may have less sensitivity tosmall variations in their level of compression (flexure) and so suchsteps may not be as beneficial. Sufficient consistency from decoupler todecoupler may be achieved in such cases by simply manufacturing them andinserting the retainer in a pre-configured location (e.g. a slot that ismilled into the pulley 24 before the biasing member 64 is inserted intothe pulley 24 against the thrust member 66. While FIG. 3 shows such anarrangement it is possible that the use of crimping or staking may bepreferable so as to provide high consistency in the biasing forceexerted by the Belleville washer 70.

It will be noted that any damping torque that is greater than theselected torque would be sufficient to keep the oscillations of the hub22 sufficiently small so as to keep the operating life of the isolationspring 28 above a desired limit. However, it will be noted that as thedamping torque increases, the wear on the friction surfaces 60 and 62increases, which could impact their operating life, and the parasiticlosses associated with use of the decoupler 20 increase. Thus, it isbeneficial to keep the damping torque as close as possible to theselected damping torque so as to achieve the intended operating life ofthe spring 28 while minimizing the wear on the friction surfaces 60 and62 and minimizing the parasitic losses associated with use of thedecoupler 20.

Reference is made to FIG. 10, which shows a decoupler 300 in accordancewith another embodiment of the present invention. The decoupler 300 iscapable of changing the amount of damping torque that is applied betweenthe pulley 24 and the hub 22. The decoupler 300 may be similar to thedecoupler 20 shown in FIG. 4, for example, employing the helicalcompression spring 72, or alternatively it could be similar to thedecoupler 20 shown in FIG. 5 or 6, or even the decoupler 20 shown inFIG. 3. The decoupler 300 includes, however, an actuator 302 thatcompresses (or more generally, flexes) the biasing member 28 by aselectable amount. The actuator 302, in the embodiment shown in FIG. 10includes an actuator drive 304 that is mounted to a fixed support memberin the vehicle, and a driven member 306 that is operatively engageablewith the biasing member 28 (e.g. by directly abutting the biasing member28). The driven member 306 may be a threaded member 308 that engages aworm gear (not shown) that is rotated by a motor (not shown) in theactuator drive 304. Rotation of the threaded member 308 selectablyadvances or retracts the threaded member 308 towards and away from thebiasing member 28, thereby providing infinite adjustment capability ofthe biasing force of the biasing member 28 over a particular range ofmovement of the threaded member. Adjusting the biasing force adjusts thedamping torque applied between the hub 22 and pulley 24. The actuator302 can be controlled to apply a high biasing force (and therefore ahigh damping torque) in situations where the decoupler 300 is incurringor is predicted to incur high torsional vibrations, and a low biasingforce (and therefore a lower damping torque) in all other situations. Inthis way, a high damping torque is applied when needed to prevent highstresses on the isolation spring 28, and a low damping torque is appliedin all other situations thereby reducing parasitic losses associatedwith the decoupler 300.

The driven member 306 in this exemplary embodiment includes theaforementioned threaded member 308, an end member 310, a bearing 312permitting relative rotation of the threaded member 308 and the endmember 310, and an actuator thrust member 314 for receiving the endmember 310 and for transmitting the force exerted by the end member 310on the biasing member 68. A seal cap is not shown in FIG. 10 so as notto obscure the other components of the decoupler 300, however, as shownin FIG. 11, the seal cap 71 may be provided, and includes a pass-throughaperture 316 that seals around the axially movable end member 310 so asto prevent the entry of contaminants into the interior of the decoupler300. Power for the actuator drive 304 (i.e. for the motor) may beobtained from any suitable source such as the vehicle battery (notshown) or from the alternator itself.

The end member 310 may be configured at its tip to have relatively lowfriction so as to inhibit heat buildup and damage to it and to thethrust member 314 when they are engaged. It will be noted that they maybe engaged during high damping torque periods, but they may be spacedfrom each other (i.e. the end member 310 may be retracted from thethrust member 314 entirely during low damping torque periods. A suitabletip treatment may be for example providing a polymeric (e.g. nylon)spherical tip, or a spherical tip that blends into a conical portion, asshown.

The actuators described herein may include electric motors as describedabove. However, it is alternatively possible to provide actuators thatare pneumatic, hydraulic or powered by any other suitable means. Forexample, it is possible to provide an actuator that is a phase changeactuator that is powered by causing a phase change in a material, suchas a wax or any other suitable material. The expansion or contraction,(depending on whether the material melted or solidified), changes theoverall volume of the material which is used to drive a member (e.g. apiston in a cylinder housing) in one direction or another. Another typeof actuator is powered by a shape memory material such as a shape memoryalloy. Where the actuators are shape memory material or phase changematerials, electrical power may be used to drive their actuation. In thecase of phase change materials, the electrical power may be used to heatthem, for example. Where the actuators are pneumatic, they may be vacuumactuators or positive pressure actuators. They may use air bladders,pneumatic cylinders, or some other suitable way of being operated. Anyof these actuators may be either linear actuators or rotary actuators.

It will be noted that some of the actuators described herein provideinfinite adjustability (e.g. actuator 302) as to the amount ofcompression is provided on the biasing member 68. It is alternativelypossible to provide an actuator that is capable of as few as twopositions for a driven member, such as a linear or a rotary solenoid, ora phase-change actuator. The two positions would include a firstposition wherein the driven member causes the biasing member 68 to exerta relatively high biasing force on the friction member 64 so as togenerate a high damping torque, and a second position wherein the drivenmember causes the biasing member 68 to exert a relatively low biasingforce on the friction member 64 so as to generate a low damping torque.

Reference is made to FIG. 12, which shows a decoupler 325 with a phasechange actuator 323 that is positioned on the pulley 24 itself. In thisembodiment, the pulley 24 has a support member 327 on it that holds theactuator 325. The actuator 323 itself may be any suitable type ofactuator, such as, for example, a phase change actuator with a piston328 and a cylinder 329 filled with a phase change material, such as asuitable wax. The piston 328 would thus constitute the driven member.Heating of the phase change material would drive the piston 328 outwardfrom the cylinder 329 to drive the thrust member 314 to compress thebiasing member 68. Cooling of the phase change material would permit thepiston 328 to be driven back into the cylinder 329 under the urging ofthe biasing member 68. To heat the phase change material, electricalpower from some source (e.g. the vehicle's battery) would be provided toa slip ring assembly 321 and transmitted therethrough to a shaft 330that extends from the back of the cylinder 329. Power from this shaft isused to heat the phase change material (e.g. via a resistive heatingelement).

While the actuator 302 permits the actuator drive 304 to be mountedremotely from the pulley 24, it may be desirable due to underhoodpackaging constraints to provide an actuator that permits greaterflexibility in the positioning of the drive. To address this, anactuator could be provided wherein the driven member is a push-pullcable, which slides within a sheath that has a free end held by abracket mounted in facing relationship to the thrust member 314. Thepush-pull cable could be driven forward through the sheath to push thethrust member 314 to compress the biasing member 68 and increase thedamping torque. The push-pull cable could be considered to be the drivenmember such an actuator. The actuator drive itself could be made up ofany suitable structure, such as a solenoid having two or more positionsthat has the push-pull cable connected thereto, or a motor and geararrangement that has the push-pull cable connected thereto.

The actuator 302 provides infinite adjustability as to the amount ofcompression is provided on the biasing member 68. It is alternativelypossible to provide an actuator that is capable of as few as twopositions for a driven member, including a first position wherein thedriven member causes the biasing member 68 to exert a relatively highbiasing force on the friction member 64 so as to generate a high dampingtorque, and a second position wherein the driven member causes thebiasing member 68 to exert a relatively low biasing force on thefriction member 64 so as to generate a low damping torque. Such anactuator could be, for example, a solenoid that is positionable in twoor more positions. The solenoid could be a linear solenoid or a rotarysolenoid.

Where availability of room is a concern, the alternator shaft itselfcould be a hollow shaft and a suitable drive could be provided at theother end of the alternator shaft (i.e. the end opposite to the end withthe decoupler 20 on it) whereby a driven member extends through thealternator shaft from the other end to the end with the decoupler.

The controller 318 may be provided to control the operation of any ofthe actuators described herein. Where controller 318 is provided, it mayoptionally operate the actuator drive based on open loop control. Forexample, the controller 318 may control the actuator based on inputssuch as engine speed, alternator status (charging or not charging), andoptionally the status of other accessories driven by the belt 14 (FIG.1). The controller 318 may position the actuator in a low- orhigh-damping torque position based on a lookup table with a map of thedifferent combinations of statuses and properties that are measured ofthe components of the engine.

Alternatively, the controller 318 may optionally operate the actuatordrive based on closed loop control. For example, sensors may be providedon several components to assist the controller 318 in determiningwhether the hub 22 is incurring or is about to incur unacceptably largetorsional vibrations. These sensors can be positioned to detect suchproperties as belt flutter, crankshaft torsional vibrations, hubtorsional vibrations, and the like. When the controller 318 detects thatlarge torsional vibrations at the hub 22 are imminent or are beingincurred, the controller 318 can operate the actuator to increase thedamping torque. While providing the high damping torque the controller318 can continue to monitor the sensor signals and can reduce thedamping torque when it detects that the belt system is stable and largetorsional vibrations are no longer imminent.

Suitable sensors can be used to detect the angular position of arotating object with high precision and thus could be used to detectangular displacements of the hub 22 and pulley 24, and of the crankshaftpulley. As noted above, a suitable sensor would be the 2SA-10 Sentronsensor manufactured by Sentron AG, Baarerstrasse 73, 630O Zug,Switzerland. Such a sensor may be capable of sensing angulardisplacement of the hub 22 by being positioned on the other end of thealternator shaft 15 (i.e. the end opposite to the end on which thedecoupler is positioned), as shown in FIG. 10. The sensor is shown at319. The controller 318 would receive signals from sensor 319.

Additionally, suitable sensors could be provided to detect the angularposition of a tensioner arm on a tensioner used to tension the belt 14.An example of a suitable sensor for this purpose is the KMZ41 sensorsold by Philips Semiconductor.

While the above description constitutes a plurality of embodiments ofthe present invention, it will be appreciated that the present inventionis susceptible to further modification and change without departing fromthe fair meaning of the accompanying claims.

Listing of Elements Element Number FIG. Engine 10 1 Crankshaft 12 1Pulley 13 1 Belt 14 1 Drive shaft 15 1 Accessories 16 1 Alternator 18 1Decoupler 20 1 Hub 22 2 Pulley 24 2 First bearing member 26 2 Secondbearing member 27 2 Isolation spring 28 2 Carrier 30 2 One-way clutch 312 Wrap spring 32 2 Outer surface 40 2 Grooves 42 2 Inner surface 43 2First (proximal) axial end 44 2 Second (distal) axial end 46 2 Firsthelical end 50 3 First end 51 2 Driver wall 52 3 Second helical end 53 2Radial wall 55 2 Sleeve 57 2 Coils 58 2 Second end 59 2 Thrust plate 732 First friction surface 60 3 Second friction surface 62 3 Frictionmember 64 3 Thrust washer 66 3 Biasing member 68 3 Retainer member 69 3Belleville washer 70 3 Seal cap 71 2 Helical compression spring 72 4Compression springs 74 5 Biasing member 76 6 Curve 80  7a Peak 82  7aPeak 84  7a Curve 86  7b Peak 88  7b Peak 90  7b Test decoupler 100 8Biasing member 102 8 Retainer 104 8 Threaded exterior surface 106 8Threaded surface 107 8 Sensor 108 8 Sensor 110 8 Controller 111 8 Hub122 8 Pulley 124 8 Bearing member 126 8 Bearing member 127 8 Isolationspring 128 8 Wrap spring 132 8 Sleeve 157 8 Friction surface 160 8Friction surface 162 8 Friction member 164 8 Thrust member 166 8 Methodstep 201 9 Method step 202 9 Method step 204 9 Method step 206 9 Methodstep 208 9 Decoupler 300 10  Actuator 302 10  Actuator drive 304 10 Driven member 306 10  Threaded member 308 10  End member 310 10  Bearing312 10  Thrust member 314 10  Pass-through aperture 316 11  Controller318 11  Slip ring assembly 321 12  Decoupler 325 12  Phase changeactuator 323 12  Support member 327 12  Piston 328 12  Cylinder 329 12 Shaft 330 12 

1. An endless drive arrangement for an engine, comprising: a crankshaftpulley mountable to a crankshaft from the engine; an alternator pulleymounted to an input shaft of an alternator, wherein the alternatoroperates at at least a first switching frequency and a second switchingfrequency; an endless drive member that is positioned to transfer powerfrom the crankshaft pulley to the alternator pulley such that firstorder vibrations are produced at the crankshaft; and a decouplerincluding a hub that is adapted to be coupled to the alternator shaftsuch that the alternator shaft co-rotates with the hub about arotational axis, a pulley rotatably coupled to the hub, the pulleyhaving an outer periphery that is positioned to engage the endless powertransmitting element, an isolation spring positioned to transferrotational force from the pulley to the hub and to accommodate torsionalvibration between the pulley and the hub, a first friction surfaceoperatively connected with the pulley, a second friction surfaceoperatively connected with the hub, a biasing member positioned to exerta bias force between the first and second friction surfaces, and aretainer engaging the biasing member to maintain the bias force, whereinthe second switching frequency is near a natural resonance frequency ofthe decoupler and the bias force between the first and second frictionsurfaces generates a damping torque during relative rotational movementbetween the pulley and the hub which attenuates said first ordervibrations so as to reduce a tendency of the alternator to operate atthe second switching frequency, thereby reducing a tendency of thealternator of transmitting vibration to the decoupler at frequenciesnear the natural frequency.
 2. An endless drive arrangement as claimedin claim 1, wherein the natural frequency is about 15 Hz.
 3. An endlessdrive arrangement as claimed in claim 2, wherein the second switchingfrequency is in the range of about 5 Hz to about 20 Hz.
 4. An endlessdrive arrangement as claimed in claim 1, wherein the damping torqueresults in a peak-to-peak angular range of relative movement between thepulley and the hub of less than about 1 degree.
 5. An endless drivearrangement as claimed in claim 1, wherein the damping torque isselected such that a peak-to-peak angular range of movement between thepulley and the hub results in at least a selected fatigue life for theisolation spring.
 6. An endless drive arrangement as claimed in claim 1,wherein the decoupler includes a one-way clutch that enables the hub tooverrun the pulley.
 7. A decoupler for an endless drive arrangementwhich includes a crankshaft-driven pulley, an alternator pulley mountedto an input shaft of an alternator which operates at at least first andsecond switching frequencies, and an endless drive member that ispositioned to transfer power from the crankshaft pulley to thealternator pulley, wherein first order vibrations are produced at thecrankshaft, the decoupler comprising: a hub that is mountable to thealternator shaft such that the alternator shaft co-rotates with the hubabout a rotational axis; a pulley rotatably coupled to the hub, thepulley having an outer periphery that is adapted to engage the endlesspower transmitting element; an isolation spring positioned to transferrotational force from the pulley to the hub and to accommodate torsionalvibration between the pulley and the hub; a first friction surfaceoperatively connected with the pulley; a second friction surfaceoperatively connected with the hub; a biasing member positioned to exerta bias force between the first and second friction surfaces; and aretainer engaging the biasing member to maintain the bias force, whereinthe second switching frequency is near a natural resonance frequency ofthe decoupler and the bias force between the first and second frictionsurfaces generates a damping torque during relative rotational movementbetween the pulley and the hub which attenuates said first ordervibrations so as to reduce a tendency of the alternator to operate atthe second switching frequency, thereby reducing a tendency of thealternator of transmitting vibration to the decoupler at frequenciesnear the natural frequency.
 8. A decoupler as claimed in claim 7,wherein the natural frequency is about 15 Hz.
 9. A decoupler as claimedin claim 8, wherein the second switching frequency is in the range ofabout 5 Hz to about 20 Hz.
 10. A decoupler as claimed in claim 7,wherein the damping results in a peak-to-peak angular range of relativemovement between the pulley and the hub of less than about 1 degree. 11.A decoupler as claimed in claim 7, wherein the damping torque isselected such that a peak-to-peak angular range of movement between thepulley and the hub results in at least a selected fatigue life for theisolation spring.
 12. A decoupler as claimed in claim 1, wherein thedecoupler includes a one-way clutch that enables the hub to overrun thepulley.
 13. A method for operating an engine accessory drive whichincludes a crankshaft-driven pulley, an alternator pulley mounted to aninput shaft of an alternator operable at a plurality of switchingfrequencies, and an endless drive member that is positioned to transferpower from the crankshaft pulley to the alternator pulley, the methodincluding: installing a decoupler for transferring torque between thealternator shaft and the endless drive member, the decoupler including(i) a hub coupled to the alternator shaft, (ii) a pulley rotatablycoupled to the hub, the pulley having an outer periphery that engagesthe endless power transmitting element, (iii) an isolation springpositioned to transfer rotational force from the pulley to the hub andto accommodate torsional vibration between the pulley and the hub, (iv)a first friction surface operatively connected with the pulley, and (v)a second friction surface operatively connected with the hub; rotatingthe crankshaft so as to rotate the engine accessory drive; generating adamping torque during relative rotational movement between the decouplerpulley and the decoupler hub by engaging the first and second frictionsurfaces with sufficient force to attenuate first order vibrations fromthe engine in order to reduce the tendency of the alternator to operateat a switching frequency near a natural frequency of the decoupler,thereby reducing a tendency of the alternator to transmit vibration tothe decoupler at frequencies near the natural frequency.
 14. A method asclaimed in claim 13, wherein the natural frequency is about 15 Hz.
 15. Amethod as claimed in claim 14, wherein the second switching frequency isin the range of about 5 Hz to about 20 Hz.
 16. A method as claimed inclaim 13, wherein the damping results in a peak-to-peak angular range ofrelative movement between the pulley and the hub of less than about 1degree.
 17. A method as claimed in claim 13, wherein the damping isselected such that a peak-to-peak angular range of movement between thepulley and the hub results in at least a selected fatigue life for theisolation spring.
 18. A decoupler as claimed in claim 13, wherein thedecoupler includes a one-way clutch that enables the hub to overrun thepulley.